<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>菜鸟教程(runoob.com)</title>
    <style>
        img
        {
            position:absolute;
            left:0px;
            top:0px;
            z-index:-1;
        }
    </style>
</head>

<body>
<h1>This is a heading</h1>
<img src="img_1.png" width="140" height="100" />
<p>因为图像元素设置了 z-index 属性值为 -1, 所以它会显示在文字之后。</p>
</body>
</html>